1. Field of the Invention
The present invention relates to an over-voltage protection device of the type which includes a plurality of stacks of series-connected, substantially identical surge arrester sections mutually electrically connected at their upper and lower ends. Each arrester section comprises an insulating casing containing a voltage-dependent resistor series-connected with a spark gap assembly. In such devices it is extremely important that the parallel-connected arrester stacks can be triggered into sharing the discharging current and the discharging energy in parallel.
2. The Prior Art
Devices for triggering parallel legs of valve resistors and spark gaps built into one and the same porcelain housing are previously known (see, U.S. Pat. No. 3,566,197). Such devices are used when a higher energy-absorbing capacity is needed than can be taken by one single leg. These known solutions are particularly used with arresters and breaking devices for high-voltage direct current, but also for alternating-current arresters for extra high voltages. In certain cases, however, there are needed more legs than can be accommodated within a given porcelain housing, and it is therefore desirable to be able to parallel-connect also a number of separate porcelain housings. Today this is of interest principally in breaker devices for high-voltage direct current (for example of the type shown in U.S. Pat. No. 3,809,959) and in devices in connection with series capacitors for achieving and maintaining an uninterrupted stabilization of the operating condition in high-voltage power supply networks (see Fahlen application, Ser. No. 536,227, filed Dec. 24, 1974, which is a streamlined continuation of Ser. No. 418,110, filed Nov. 21, 1973). It was previously known to parallel-connect several separately arranged stacks of arrester sections U.S. Pat. No. 2,608,600), but the triggering system which is used there presupposes that the different arrester sections in a stack have different resistance values. From a practical and economical point of view, however, this is a disadvantage, and therefore solutions where the arrester stacks can be modulized are aimed at, that is where stacks can be built up of sections (modules) which are mainly exactly alike.